The present invention relates to a magnetic tape drive unit for use in data processing and computer applications, and in particular to a low-profile horizontal type of open-reel magnetic tape drive unit in which the magnetic tape is threaded from the tape reel to the take-up hub completely automatically, after the reel is inserted. The method of automatic threading is such that it is not necessary to hermetically seal the unit, and in fact such a magnetic tape drive unit can be operated equally well with or without a cover, and so can be mounted in any of a variety of ways. For example, the unit can simply be placed horizontally within a drawer.
There is a need at present for an automatic tape threading type of magnetic tape drive unit for use in data-processing and computer applications which would have a simple mechanical configuration, for reduced manufacturing cost, and could be disposed horizontally (i.e. with the tape running along a substantially horizontal path) so that the unit has a low profile, suitable for rack mounting or drawer mounting. The need for an automatic threading capability is due to the fact that manual threading of the tape in such units will frequently result in damage to the tape, and moreover is extremely time-consuming for the operator. Manual threading can of course be eliminated if the tape is disposed within cassettes, such as are widely used for video recording. However this leads to a very considerable increase in the amount of space required for storing the tapes, and hence is highly undesirable. The need for a low profile is self-evident, since almost all of the other components of a data-processing installation are of an essentially flat, horizontal shape, and a vertical configuration is basically incompatible with drawer or rack mounted equipment. Various types of automatic-threading magnetic tape drive units are known in the prior art. However most of these are of a vertical configuration, which is undesirable for the reasons discussed above, and have a generally complex mechanism which is expensive to manufacture. The basic reason for the use of an upright configuration is that this enables the action of gravity on the tape to be employed, to assist in guiding the tape along a desired route in conjunction with other means such as air jets.
An automatic-threading magnetic tape drive unit having a horizontal configuration has been described by Peter et al (U.S. Pat. No. 4,243,186). This utilizes suction, created at the take-up hub of the unit, to produce a current of air flowing from the exterior and along a path from the tape reel to the take-up hub. As stated in the Peter et al specification, such a system utilizes an air flow having a high rate of flow at low pressure. With such a magnetic tape drive unit, it is necessary to hermetically seal the unit by a cover, to ensure that the air flow is directed only along the desired path such as to transport the free end of the tape to the take-up hub, when automatic threading of the tape is being performed. In addition, due to the large rate of flow which is necessary, the equipment (i.e. blower fan, fan motor, etc.) used to produce the suction must be relatively large, so that the overall size of the magnetic tape drive unit cannot be made extremely compact with a very low profile. Furthermore, it is a basic disadvantage of such an air suction type of magnetic tape drive unit that the air flow has no inherent effect tending to direct the free end of the tape along the center of the tape transport path (i.e. the vertical-walled channel within which the tape runs between the tape reel and the take-up hub). Thus it is found in practice with such a system that the free end of the tape tends to adhere to the walls of the tape transport path, or that the tape tends to become twisted, as it is being led towards the take-up hub, so that correct automatic threading operation cannot be reliably attained. Moreover it is found that with such a system it is difficult to ensure that the free end of the tape will be reliably wound onto the take-up hub, after it has been transported thereto by the air flow along the tape transport path, and the tape may be damaged when it is wound onto the take-up hub.
There is therefore a requirement for a horizontal type of open-reel magnetic tape drive unit which will perform automatic threading of the tape from a reel along a predetermined path (having a magnetic read/write head disposed at some point on that path) to a take-up hub, and automatic winding of the tape onto the take-up hub, in a reliable and accurate manner without damage to the tape or any need for manual intervention. It is also a requirement for such a magnetic tape drive unit that the overall configuration, preferably including means whereby a tape reel is automatically clamped onto a drive shaft when it is inserted into the unit, be simple and easily manufactured at low cost. Such requirements are not met by prior art types of magnetic tape drive units.